Virus-specific CD4 and CD8 T cell responses are important in controlling HIV replication, but in most infected individuals these responses are inadequate to fully contain the virus. Emerging data indicate that there is a functional loss in cellular immune responses as HIV disease progresses, suggesting that efforts to augment immunity may provide a therapeutic benefit. Dendritic cells (DCs) are the most potent antigen presenting cells, and when manipulated ex vivo to express viral antigens these cells can efficiently boost T cell responses in humans after re-injection. One of the most promising methods of delivering antigen to DCs is by transfection with mRNA encoding specific immunogens, which has been shown in human cancer studies to induce CD4 and CD8 responses to those antigens. This new method allows delivery of autologous HIV sequences to DCs, which may provide a unique advantage in augmenting virus-specific immune responses in an infected individual. Thus, we believe that vaccination with DCs transfected with autologous HIV mRNA is a promising approach to immune-based therapy. Our specific aims in this proposal are to: 1) Define the optimal method of delivering autologous HIV antigens to DCs to elicit strong and diverse virus-specific CD4 and CD8 immune responses. This work will focus on mechanisms of antigen presentation, including issues of immune interference, the effect of subcellular compartmentalization of antigen on immunogenicity and the effect of a costimulatory molecule, OX40 ligand, on DC function; 2) Clone autologous HIV mRNA transcripts from infected individuals with suppressed virus loads for transfection into DCs; and 3) Test the safety, immunogenicity and antiviral effect of this method of inducing immune responses against autologous HIV antigens by conducting a clinical trial of mRNA-transfected DCs in HIV+ subjects who have suppressed virus loads on antiretroviral therapy. Relevance of this research to public health: This work will lead to a better understanding of how to boost immune responses against HIV using a new method of vaccination. By understanding the mechanisms by which immune responses against HIV can be augmented, this may lead to improved ways of treating this disease and may help in developing a vaccine to prevent this infection.